1. Field of Invention
The present invention relates to a method for manufacturing a polarization beam splitter.
2. Description of Related Art
Compact polarization beam splitters have been employed in an apparatus using a particular polarized beam, such as a projector employing a liquid-crystal display apparatus. FIG. 9 is a perspective view showing such a polarization beam splitter. The polarization beam splitter 70 has a structure having triangular and square prisms 71, 73, and 74, between which a polarization beam separating film 75 and a reflective film 76 are alternately sandwiched. The polarization beam separating film 75, constructed of an inorganic multilayer, is arranged between the prism 71 and the prism 73. The reflective film 76, constructed of an aluminum multilayer or an inorganic multilayer film, is arranged between the prism 73 and the prism 74. When a randomly polarized beam 77 is incident on the prism 72, the beam 77 is split into a P-polarized light component and an S-polarized light component. The P-polarized light component is transmitted through the polarization beam separating film 75 and then the prism 71 and exits outwardly. The S-polarized light component 78 is reflected from the polarization beam separating film 75, enters the prism 73, is reflected from the reflective film 76, and then exits outwardly. The polarization beam splitter 70 has the function of splitting the incident beam into two types of linearly polarized beams. With a wavelength film arranged on the exit surface of the polarization beam splitter, a polarizing beam converter for aligning the two types of polarized beams into one type of polarized beam is constructed. The polarizing beam converter is used in an apparatus handling a particular polarized beam to increase the utilization of light.
The polarization beam splitter 70 shown in FIG. 9 is manufactured in a method shown in FIG. 10. A planar polarization beam splitter block 70a having a generally parallelogrammatic shape in cross section is first manufactured. The polarization beam splitter block 70a has a structure in which a plurality of prisms are glued to each other, each having a parallelogrammatic shape in cross section. The prisms on both ends of the block are cut to form a triangular prim, thereby forming a rectangular parallelepiped polarization beam splitter. Such a cutting step is required because the rectangular parallelepiped shape is easy to assemble into an optical apparatus such as a projector.
In the cutting step, the polarization beam splitter block 70a to be cut is fixed to a support stand. The cutting step is performed by bring a toothed blade close to the polarizing beam splitter block to the side thereof opposite to the support stand. The cutting operation may be conveniently performed from the same side of the block regardless of which end of the block is cut.
If the block is cut from the same side as shown in FIG. 10, the toothed blade must cut into an edge of the parallelogram in cross section on one end of the polarization beam splitter block (the left end in FIG. 10). Such a cutting operation is subject to a cutting path slipping toward the ramp of the parallelogram as the cutting is in progress.
The present invention provides a cutting method of a polarization beam separating material which suffers from less cutting path slipping. Specifically, a laminate is constructed by gluing a plurality of substrates, at least some of which have a polarization beam separating film on one surface thereof. The planar laminate of the substrate is cut at a predetermined angle to the surface thereof to form a generally planar polarization beam splitter block in which a plurality of prisms are glued, each having a parallelogrammatic shape in cross section. A generally rectangular parallelepiped polarization beam splitter is thus formed by cutting away a prism portion having a generally trapezoidal shape in cross section from at least one end portion of the polarization beam splitter block.
In this embodiment, the prism portion having a generally trapezoidal shape in cross section is cut away from one end portion of the planar polarization beam splitter block in which the plurality of prisms are glued to each other, each having a parallelogrammatic shape. For this reason, the toothed blade is allowed to cut into a flat portion of the planar polarization beam splitter block during the cutting operation. This arrangement reduces the possibility of slipping the cutting path. Because of its generally rectangular parallelepiped shape, the polarization beam splitter is easy to assemble in a diversity of apparatuses.
Preferably, the width across the upper surface of the cut portion having the generally trapezoidal shape in cross section is larger than half the thickness of a toothed blade. With this arrangement, the outward face of the toothed blade comes inside the edge of the surface of the polarization beam splitter block. The effect of reducing the possibility of slipping the cutting path of the toothed blade is further increased.
In the step for forming the laminate, the thickness of, at least, one of the two outermost substrates of the laminate is larger than the thickness of one substrate glued between the two outermost substrates, and in the step for cutting away a prism portion having a generally trapezoidal shape in cross section, the cut portion is preferably cut from the outermost substrate of the laminate having the larger thickness.
When the laminate is cut to form the polarization beam splitter block, the outermost substrate of the laminate forms a prism of the end of the polarization beam splitter block. With this arrangement, the cross-sectional area of the end prism is enlarged. In the third step, the prism having a generally trapezoidal shape is cut away.
In the step for cutting the prism having a generally trapezoidal shape, the two ends of the polarization beam splitter block are cut, and the toothed blade cuts from one side of the planar polarization beam splitter block.
With the above arrangements, a simple cutting facility works. Specifically, placing the polarization beam splitter block upside down during the cutting operation is not necessary. There is no need for a facility which is equipped with toothed blades on both sides of the polarization beam splitter block. By sending the same toothed blade twice in different positions, the two end portions are cut away from the polarization beam splitter block. In the step for cutting the two end portions of the polarization beam splitter block, the toothed blade cuts into in the vicinity of the edge where the end face and the top surface of the polarization beam splitter block intersect. In such a case, there is a possibility that the cutting position of the toothed blade slips toward the end face. With the arrangement of the present invention, however, the toothed blade cuts into the top surface of the prism having the trapezoidal shape, and the possibility of slipping the cutting path is low.
The present invention can be embodied in the following diverse aspects, for example:
(1) A manufacturing apparatus for manufacturing a polarization beam splitter.
(2) A manufacturing method for manufacturing a polarization bean splitter.
(3) A computer program for operating the manufacturing apparatus or carrying out the manufacturing method.
(4) A storage medium for storing the computer program which operates the manufacturing apparatus or carries out the manufacturing method.
(5) A data signal, including the computer program which operates the manufacturing apparatus or carries out the manufacturing method, and modulated by a carrier wave.